Copolymers of ethylene and acrylate esters and methods for their manufacture have been reported in the literature, such as in U.S. Pat. No. 2,200,429, U.S. Pat. No. 2,953,551 and U.S. Pat. No. 3,350,372. The '372 patent to Anspon discloses an ethylene acrylate ester copolymer wherein the acrylate esters include, for example, methyl acrylate, 2-butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, octadecyl acrylate and the corresponding esters of methacrylic acid. The '372 patent states that preferred copolymers contain a maximum of 0.5 mole of acrylate ester per mole of ethylene, i.e., 33 mole percent acrylate ester, and that the copolymers ordinarily will contain at least 1 mole percent of the acrylate ester and preferably will contain 0.025-0.20 and more especially 0.05 to 0.15 mole of acrylate ester per mole of ethylene. For ethylene-methyl acrylate copolymer ("EMA"), 0.50 mole of acrylate per mole of ethylene would be approximately 60 weight percent methyl acrylate based on EMA copolymer, and 0.20 mole of acrylate per mole of ethylene would be approximately 38 weight percent methyl acrylate.
U.S. Pat. No. 3,756,996 to D. W. Pugh et al., which is hereby incorporated by reference in its entirety, discloses an apparatus and method for polymerizing ethylene and other monomers in a multi-zoned reactor system.
These ethylene-alkyl acrylate ("EAA") copolymers have been excluded from some markets because the melt-point temperature has been lower than what the market required of the EAA copolymer having a given amount of alkyl acrylate. As more alkyl acrylate was incorporated into the copolymer to make the copolymer more rubbery, the melt-point temperature of the copolymer decreased sharply.
In addition, EAA copolymers have been excluded from other markets because EAA copolymers have not had sufficient adhesive strength to, e.g., layers or films of other polymers to bind the EAA and other polymers strongly enough to prevent delamination. The present invention provides EAA copolymers with improved melt-point temperature and/or improved adhesive strength, and a method for making these copolymers.